Thank you Über--
My memory is evidently hazy, because I remember having problems with the smoke unit on my 681--which I finally sent out to Mr Chuck Sartor in Denver--but I didn't recall smoke issues with my 682. Aside from the apparent non-smoking, the 682 had problems running in general a few years back, and I was discouraged when my local repair shop did a so-so job, as referenced in the thread you hyperlinked where one of the rivets popped off and the other was only hand-tight upon return. One aspect that I did clearly remember is that the side piston valves are not to be messed with...
At any rate, the thread doesn't state how the smoking issue was finally resolved. I know that it has been smoking perfectly for the past few years, and my local guy--one hour away--snapped at me this morning when I called and asked if he will be in tomorrow/Saturday (Him: "It's the holiday season crunch time and I cannot drop everything to tear down your engine." Me: "Fair enough, but when I drove out there Monday morning with it, I told you about the smoking issue but you didn't address it"). Not that I was looking forward to spending my Saturday making a second trip in the same week for a train repair, but that sealed it.
I suppose I will send this one to Mr Sartor as well. Over the past 5 years, I am sure that in repair and re-repair costs I have far exceeded the resale values of my 681 and 682. It's only money.